Detachable anchor bolts



April 5, 1966 F. SCHUERMANN ETAL 3,244,055

DETACHABLE ANCHOR BOLTS Original Filed March 15, 1961 2 Sheets-Sheet 1@mmm Edwina/QM amp April 5, 1966 F. SCHUERMANN ETAL 3,244,055

DETACHABLE ANCHOR BOLTS Original Filed March 15, 1961 2 Sheets-Sheet 2/NVENI'0,PS 7' @ZA Wu 4). Jim

United States Patent 3,244,055 DETACHABLE ANCHOR BOLTS FritzSchuerrnann, Baimlerstras'se, Essen-L redeney, Germany, and RudolfNovotny, 22 @stpreussenstrasse, Essen-Heisingen, Germany Continuation ofapplication Ser. No. 95,925, Mar. 15, 1961. This application Mar.26,1964,Ser.N .sssnza 2 illaims. (Cl. 85-1) This is a continuationapplication of an earlier filed application Serial Number 95,925, filedMarch 15, 1961, now abandoned.

This invention relates to anchor bolts which are used, for example, forthe support of mine workings, for securing overhanging rock walls aboveground and in building for reinforcing foundations or the like.

Such anchor bolts are secured by their tips in the bottoms of drillholes and are braced against the rock or the like by means of a platesecured to that end of the bolt which projects from the drill hole.

Substantially more advantageous than purely mechanical fixing, which isconventionally obtained in anchor bolts by forcing an expansible tipagainst the wall of the drill hole, is a recently developed method inwhich securing of the tip of the anchor .bolt in the bottom of the drillhole is effected by cementing the same in the hole by means of cement,cement mixtures or hydraulic mortar introduced into the drill hole infront of the anchor bolt, for example by a pressure pipe or in acartridge contain ng synthetic resin, hardener and accelerator in aplurality of compartments. In the known method, the cartridge isdestroyed by the tip of the anchor bolt penetrating into it when theanchor bolt is introduced into the hole, preferably with a rotatingaction, so that intimate mix ng of the synthetic resin, hardener andaccelerator and, thereby, rapid hardening of .the previously visconsresin occurs. This method of securing an anchor bolt in the bottom of adrill hole allows the use of bolts of substantially simpler design thanthe conventional expansible bolts and permits a cementing of the anchorbolts in the drill holes so that the release thereof, i.e. laterwithdrawal of the bolts, is generally impossible.

The invention relates to anchor bolts secured by cementing material inthe bottom of a drill hole. According to a first feature, the object ofthe invention is to permit removal of at least part of the anchor bolt.According to the invention, this is achieved in that the anchor boltconsists of two parts, a tip and a shank extending beyond the mouth ofthe drill hole, which are detachably connected to one another by meansof screw threads, a coupling or other connecting elements having areversible action, the location of the connection of the .parts beingsuch that the tip is shorter than one half of the total length of theanchor bolt.

The proportioning of the length of the tip While maintaining said lengthshorter than one half of the length of the complete anchor bolt dependsmainly on the length of the cementing or adhesion surface provided inthe bottom of the drill hole. Generally, the length of such cement ngsurface in the method in which the constituents of the cement areintroducedinto the bottom of the drill hole in a destructible cartridgeis between -40 cm. according to the rock conditions. As the normal totallength of an anchor bolt is at least two meters, it is possible torecover practically 80% of the anchor bolt, that part (the shank) whichhas been screwed out being immediately ready for use again by screwingon a new tip, and thus to reduce the cost of anchor-bolt supports by thecementing method by 40-60%.

Another advantage which is obtained in the cementing method owing to thetwo-part construction of the an- 3,Z44,55 Patented Apr. 5, 1956 chorbolt according to the invention is the possibility of screwing bolt tipsof suitable diameter and length, which may be varied as desired, on tothe longer section or shank of the anchor bolt.

The diameter of that part of the bolt which is disposed towards themouth of the drill hole is thus entirely independent of the diameter ofthe drill hole, so that the latter is no longer subiect to limitationsbecause of considerations of the amount of material in the anchor boltand can therefore be enlarged, which enables an enlargement in the areaof adhesion for the same cementing-in length of the tip or thepossibility of making the cementing-in length smaller. In addition, thedetrimental effect of the expansion of a steel anchor bolt on thecementingin length, .i.e. the loss of effective cementing-in length,which increases with the expansion, is eliminated if a screwed-on tipmade of a cast steel which expends very little is employed. The resultis that the available cementing-in length is utilized to substantiallybetter advantage than heretofore and this also can result in a reductionin the length of the cartridge and thereby of the cost thereof.

The detachable tip may consist of material other than that of the mainpart of the anchor b0 t, for example of a polyester resin, a phenolicresin or the like reinforced with glass fiber, which results in improvedadhesion of the tip to the synthetic resin introduced into the drillhole as the cementing material. It is also possible to manufacture theshank which is to be recovered of synthetic resin.

The anchor bolt tip, which may be provided with an external thread toenable it to be screwed into the synthetic resin contained in the bottomof the drill hole or into a cartridge filled with resin, may have sosmall a length that, when it is manufactured from synthetic resin, itcan readily be made by conventional molding or injection method.

The complete independence of the tip of the anchor bolt from the mainpart of the latter makes it possible to incur heavier expenditure forthe manufacture thereof, without the cost of tie complete anchor boltbecoming uneconomic, and so to design the bolt that optimum conditionsare obtained for the cementing thereof in the bottom of the drill-hole.

To this end the tip of the anchor bolt may be provided, in the region ofthe tip to be secured in the drill hole, with encircling thread-likeribs and at its free end with a conical point. Longitudinal grooves maybe provided to extend from the conical point over the entirecementing-in length or a part thereof, the grooves having a depth atleast equal to that of the thread-like ribs, so that the longitudinalgrooves interrupt theperipheral extension of said ribs.

With this design, the penetration of the tip of the anchor bolt withrotary action into the cartridge takes place with the smallest possibleresistance and, after the cartridge has been destroyed, the chargethereof is moved by the conical point of the tip mainly transversely ofthe direction of the penetration of the tip andtowards the wall of thedrill hole, without an undesirably high pressure being generated in theundestroyed part of the cartridge to oppose the tip penetration.

Even in the event of the cartridge being already completely destroyedwhen the tip of the anchor bolt first strikes it, the major portion ofthe cementing material is still pressed against the wall of the drillhole and only a small quantity thereof is compressed against the bottomof the drill hole.

The spiral turns on the tip act as a scr w press which compresses thecementing mixture towards the bottom of the drill hole, but the grooveswhich extend longitudikeying surfaces.

7 partying nally of the tip and interrupt the ribs in the peripheraldirection prevent this pressing action becoming undesirably 'drill holeintercepts cracks and fissures into which the cementing material couldpenetrate too far on being strongly compressed so that the amount ofcementing material left in the bottom of the drill hole would no longerbe sufficient to fill the cavity.

In addition to the longitudinal slotshaving the effect of achieving acertain equalization of pressure between the bottom of the drill holeand the adjacent region of the periphery of .the hole which is to becemented to the anchor bolt, they also act to improve the mixing whenthe tip of the anchor bolt is screwed into the cartridge.

As small a pitch as possible of the thread formed by the encirclingspirals has been found to be desirable to avoid an undesirable increasein pressure, and the pitch is preferably of the order of magnitude ofbetween 2 and mm., preferably 3 mm., per turn. With this small pitch,even when the directionof rotation of the thread and of the shank arethe same, the compression of the cementing materialin the bottom of thedrill hole does not exceed a desired value when the tip is introduced.

When opposite directions of rotation of the thread and shank are used,the rotation of the anchor bolt has the effect of conveying thematerialaway from the bottom of the drill hole, i.e., so that, ifdesired, all compression of the cementing material in the bottom of thedrill hole can be avoided.

The invention also provides the possibility of applying, when the anchorbolt has penetrated almost completely into the cartridge and the mixingof the constituent has been completed, an increase in the compressingpressure which may then be desirable by means ofv a disc mounted on theanchor bolt so as to seal off the space in the drill hole which isfilled with the cement and to prevent the cement flowing down inupwardly directed drill holes. The disc is arranged at so small adistance from the tip of the anchor bolt that, after the cavitysurrounding the tip of the anchor bolt has been completely filled withthe cement, the disc acts on the latter as a piston as the anchor boltis further screwed in, the disc compressing the cement evenly in thedirection of the bottom of the drill hole.

The design of the tip of the anchor bolt described above is alsoadvantageous if the tip is not detachably connected to the shank butforms one structural part therewith.

The above-described manifold possibilities, provided by the design ofthe tip of the anchor bolt in accordance with the invention, of varyingthe pressure efiect on the cebottom of the drill hole, are dependent toa considerable extent on the uniformityof the rotating or strikingmovement imparted to the anchor bolt when it is driven in.

4 In FIGURE 1 the reference 1 indicates the tip anchor bolt whichisdetachably connected to the shank 2 of the anchor bolt by means ofarscrew thread 3; the tip 1 terminates in a conical point 9 having asemi-spherical.

angle of about To improve the adhesion and the mixing effect when thebolt tip 1 is screwed into a cartridge containingthe plastic, the tip 1comprises, over the major part of'it s length, an external thread 4 and,adjacent its rear end, an annular groove 5 in which an annular disc 6 isinserted for sealing off the bottomof the drill hole which is filledwith the cement. The sealing disc 6 preferably consists of hard rubberor a material equivalent thereto and is of According to the preferredembodiment of the invention, the disc 6 is ar the same diameter as thedrill hole;

ranged at such'a distance from the point 9 that, after the cartridgecontaining the constituents of the cement has been completely destroyed,the disc 5 exerts a compressing pressure on the mixture contained in thebottom'of the drill hole when the anchor bolt is further screwed in.

The shank '2 is provided at its outer end with a thread 7 which enablesthe anchor bolt to be braced against the rock by means of a base plateand nut. The shank terminates in a squared ends with a plain base or endsur-- face 3- on which a device which turns the anchor bolt,

i.e., screws it in when it is being set and screws the shank 2 out whenit is being removed, can act. The plain base or end surface 8' alsoenables the anchor bolt to be driven in by means of a hammering actionon saidend surface instead of with a rotating action.

FIGURES'Z and 3 showeven more clearly than does FIGURE 1 the externalthread on the tip 1 with a pitch of the turns of between 2 and 10 mm.The turns may be either left-handed or right-handed, i.e., they may beformed so that they correspond to the direction of rotation of theanchor bolt when it is driven in or are opposite to said direction ofrotation.

The spiral thread turns are interrupted by a plurality of longitudinalgrooves 10 distributed uniformly over the periphery and of a depth atleast equal to the depth of the turns 4 of the thread. If required, thegrooves may of the drill .hole which is to be filled with cement or.

- mortar mixture. The disc 6' is mounted, prefer-ably ee- According to afeature of the invention, in order to obtain such uniformity and for thepurpose of transmitting movements from a rotary tool, for example arotary drilling machine, employed for the drive, keying surfaces areprovided on that part of the anchor bolt which projects from the drillhole and keys, spanners, or sockets which a can be inserted in the headof the tool are engaged on said The presence of these keying surfaces 7anchor bolt constituting a first embodiment,

FIGURE 2 is a similar view to FIGURE 1 of a second embodiment, and

FIGURE 3 is a similar view of a third embodiment.

merited, on the tip at a distance from the point 9 which is chosen independence on the cementing-in length of the tip provided with a thread.a

The embodiment shown in FIGURE that shown in FIGURE 2 only in that thelongitudinal grooves 10 do not extend beyond the sealing disc 6", butare arranged only in the front region of the anchor bolt, i.e. only on apart of the intended cementing length, and

act to produce an equalization of pressure over this most importantregion.

In FIGURE 3, the direction of twist of the spiral turns ferentiation'ofthe adhesion of the cement mixture to the; a

periphery of the tip as compared with its adhesion to the wall of thedrill hole, as a result of which, if a certain I loading of the bracedanchor bolt is exceeded, the adhesion of the cement mixture ceases inthe region of this of an differs from plain part, whereas it ismaintained at the wall of the drill hole, so that the cement mixture iscompressed elastically and compacted transversely of the direction ofthe anchor bolt.

The invention is not limited to the embodiments described in detailabove and illustrated in the drawings, and numerous modificationsthereof are possible without departing from the scope of the followingclaims. Thus, in particular, the design of the tip of the anchor boltaccording to FIGURES 2 and 3 is also applicable with similar advantagesto anchor bolts whose tip part is not separable from the shank of theanchor bolt.

What we claim is:

1. In an anchor bolt assembly adapted to support mine workings, rockwalls, foundations and the like by being secured in a drill hole havinga transverse cross sectional dimension larger than the transverse crosssectional dimension of the anchor bolt assembly by means of a cementingmaterial, said assembly including:

an anchor bolt tip portion and a shank portion detachably securedthereto, said tip portion being generally cylindrical and terminating atone end in a cone, the other end of said tip portion having an internal-1y threaded bore, an external helical cement material mixing grooveextending from the cone of said tip portion toward the said other end ofsaid tip portion, at least one external longitudinal groove extendingfrom the cone of said tip portion toward said other end and terminatingwithin said mixing groove, said helical mixing groove intersecting saidlongitudinal groove and together forming flow and mixing channels forthe cementing material, a sealing washer disposed outwardly beyond saidlongitudinal groove, said sealing washer including a pair of threadednuts threadably engaging the helical groove with an annular sealingmember therebetween;

and said shank portion including a threaded portion at one end adaptedto be threadably received in the internally threaded end of the tipportion, and means at the other end of said shank portion for rotatingthe assembly in a drill hole.

2. In an anchor bolt assembly adapted to support mine workings, rockwalls, foundations and the like by being secured in a drill hole havinga transverse cross sectional dimension larger than the transverse crosssectional dimensicn of the anchor bolt assembly by means of a cementingmaterial, said assembly including:

an anchor bolt tip portion and a shank portion detachably securedthereto, said tip portion being generally cylindrical and terminating atone end in a cone, the other end of said tip portion having a smoothcylindrical outer wall surface and an internally threaded bore formedcoaxially thereof, an external helical cement material mixing grooveextending from the cone of said tip portion toward the said other end ofsaid tip portion, at least one external longitudinal groove extendingfrom the cone of said tip portion toward said other end and terminatingin the smooth cylindrical outer wall surface inwardly of the outermostend thereof, said helical mixing groove intersecting said longitudinalgroove and together forming flow and mixing channels for the cementingmaterial, sealing means secured to the smooth cylindrical outer wallsurface and disposed inwardly of the termination of said longitudinalgroove; and said shank portion including a threaded portion at one endadapted to be threadably received in the internally threaded end of thetip portion, and means at the other end of said shank portion forrotating the assembly in a drill hole.

References Cited by the Examiner UNITED STATES PATENTS 569,235 10/ 1896Rockwell --14 2,573,498 10/1951 Scott 85-82 2,690,879 10/ 1954 Snyder85--23 2,829,502 4/1958 Dempsey 85-23 2,890,845 6/ 1959 Kiekhaefer.

FOREIGN PATENTS 3,012 2/ 1889 Great Britain. 70,309 6/ 1915 Switzerland.

CARL W. TOMLIN, Primary Examiner.

2. IN AN ANCHOR BOLT ASSEMBLY ADAPTED TO SUPPORT MINE WORKINGS, ROCKWALLS, FOUNDATIONS AND THE LIKE BY BEING SECURED IN A DRILL HOLE HAVINGA TRANSVERSE CROSS SECTIONAL DIMENSION LARGER THAN THE TRANSVERSE CROSSSECTIONAL DIMENSION OF THE ANCHOR BOLT ASSEMBLY BY MEANS OF A CEMENTINGMATERIAL, SAID ASSEMBLY INCLUDING: AN ANCHOR BOLT TIP PORTION AND SHANKPORTION DETACHABLY SECURED THERETO, SAID TIP PORTION BEING GENERALLYCYLINDRICAL AND TERMINATING AT ONE END IN A CONE, THE OTHER END OF SAIDTIP PORTION HAVING A SMOOTH CYLINDRICAL OUTER WALL SURFACE AND ANINTERNALLY THREADED BORE FORMED COAXIALLY THEREOF, AN EXTERNAL HELICALCEMENT MATERIAL MIXING GROOVE EXTENDING FROM THE CONE OF SAID TIPPORTION TOWARD THE SAID OTHER END OF SAID TIP PORTION, AT LEAST ONEEXTERNAL LONGITUDINAL GROOVE EXTENDING FROM THE CONE OF SAID TIP PORTIONTOWARD SAID OTHER END AND TERMINATING IN THE SMOOTH CYLINDRICAL OUTERWALL SURFACE INWARDLY OF THE OUTERMOST END THEREOF, SAID HELICAL MIXINGGROOVE INTERSECTING SAID LONGITUDINAL GROOVE AND TOGETHER FORMING FLOWAND MIXING CHANNELS FOR THE CEMENTING MATERIAL, SEALING MEANS SECURED TOTHE SMOOTH CYLINDRICAL OUTER WALL SURFACE AND DISPOSED INWARDLY OF THETERMINATION OF SAID LONGITUDINAL GROOVE; AND SAID SHANK PORTIONINCLUDING A THREADED PORTION AT ONE END ADAPTED TO BE THREADABLYRECEIVED IN THE INTERNALLY THREADED END OF THE TIP PORTION, AND MEANS ATTHE OTHER END OF SAID SHANK PORTION FOR ROTATING THE ASSEMBLY IN A DRILLHOLE.